The present invention relates generally to two component mixers and sprayers and more specifically to an internal mixer and sprayer capable of being used with any two component systems and specifically for polyester foams and resins.
Fiberglass spraying devices, and particularly hand held units, have previously employed a number of different spraying methods in attempts to provide well-mixed, properly shaped fluid spray flows in the most efficient manner possible. Typical fiberglass spraying apparatus supply fluid resin and fluid catalyst to a nozzle for internal or external mixing. With internal mixing, catalyst fluid may typically first be atomized by mixing with air and then directed into the path of the fluid resin at the nozzle interior. After resin-catalyst mixing, the resulting fluid is forced through a common nozzle and directed at the work piece. Internal mixing requires time consuming and expensive cleaning of the nozzle and mix chambers after each use.
With external mixing, both catalyst and resin fluids may typically be forced though separate spray nozzles prior to mixing. These nozzles are directed such that the catalyst and resin spray flows intersect to permit mixing prior to contact with the work piece. If the resin is not atomized prior to spraying, the process is often called "airless." Such external mixed sprayers may not need extensive cleaning after each use, but typically require high fluid pressures. Reinforcing fibers may typically be directed into the mixed spray path of either internal or external mix sprayers to be wetted thereby and carried to the work piece.
The difference between paint spraying and resin spraying has been recognized by many including the state of California which enacted a new rule 1162 directed to polyester resin operations. This rule defines what comes under the statute as well as the special health compliances. Polyester resin spray facilities must be in compliance by July 1, 1988.
For emission control as well as waste purposes, it is desirable to use an internal mix which uses the minimum amount of catalyst or resin. A polyester foam which cures faster and is safer environmentally has been developed by Alpha Corporation. The Alcel polyester foam has a high viscosity in the range of 3600 centipoise compared to 300 centipoise for normal sprayable resins. To produce a foam in the range of 25 to 30 pounds per cubic foot, 3% of blowing agent and 2% of catalysts are added to the Alcel polyester resin. Alcel also offers a filled resin with 40% filler and 60% foam having a viscosity in the range of 120 centipoise. The suggested use is 1.75% of blowing agent and 1.25% catalyst by compound weight. This produces a density in the range of 40 to 50 pounds per cubic foot.
In order to internally mix polyester foams and resins the prior art has used high pressure to force the catalyst and blowing agent into the resin and thus, required substantially long restrictors and surge tanks. The resin and catalyst are introduced at high pressures in opposite directions towards each other to begin the mixing. Similarly, they required static mixers to assure mixing of the catalyst and blowing agent with the resin. Additionally, the catalyst has been provided at four to seven times the pressure of the resin to assure mixing. When the nozzle size or primary material pressures were changed, the system had to be totally rebalanced. Examples of these types of spray guns and systems are shown in U.S. Pats. Nos. 3,709,468 and 3,790,030.
Thus, it is an object of the present invention to provide an improved airless, internal mix sprayer for mixing a small amount of catalyst or secondary fluid to a large amount of primary fluid wherein the mixing balance is self adjusting.
Another object of the present invention is to provide an internal mixer which is capable of operating at reduced supply pressures.
Another object of the present invention is to provide an internal mixer without static mixers.
A still further object of the present invention is to provide an internal mixer for primary and secondary fluids without the need for substantial restriction and surge tanks in the secondary supply lines.
A still even further object of the present invention is to provide an internal mixer which is self-balancing for the changing of spraying nozzle sizes and pressures.
A still even further object of the present invention is to provide a cartridge which is mounted to the face of an existing gun to provide internal mixing of fluids.
These and other objects of the present invention are achieved by introducing a secondary fluid or catalyst radially into a first axial bore and introducing a primary fluid or resin axially to flow through the secondary fluid to be mixed therewith. Preferably the secondary fluid is introduced radially with a circumferential rotation and the primary fluid is introduced as an axial annulus. This allows the system to be self-balancing and the secondary fluid to be introduced at a relative low pressure. The secondary fluid is introduced through a circumferential orifice which is sufficiently small such that there is a pressure change produced by the flowing primary fluid such that the ratio of inlet pressure of the secondary fluid to primary fluid remains substantially constant for variations of flow rates. A substantially short annular restrictor is used in the secondary fluid inlet to prevent surges and act as an accumulator.
The primary fluid is introduced through the interior of a reducing element and then radially to its exterior to form an axial annulus. The reducing element extends from an axial position at which the primary fluid is introduced radially past the axial position at which the secondary fluid is introduced to form a first annular passage. A dispersing chamber is provided axial between the reducing element and the spray nozzle of a substantially larger cross-sectional area than the cross-sectional area of the primary annulus to further mix the primary and secondary fluids by turbulence produced by the change of cross-sectional area.
The secondary fluid from the secondary fluid inlet is introduced tangentially to a second annular passage connected to the circumferential orifice to produce the circumferential rotation of the secondary fluid at the circumferential orifice. The cross-sectional area of the second annular passage is larger at the point of introduction from the inlet than the cross-sectional area where it is connected to the circumferential orifice. The width of the circumferential orifice is smaller than the cross-sectional area of the second annular passage.
An air nozzle is provided adjacent to the spray nozzle for producing an axial flow for maintaining a substantially homogeneous mixture of primary and secondary fluids and/or further shaping of the spray pattern. The primary fluid may be a polyester resin or a foaming polyester resin which is premixed in a mixing chamber before being introduced to the first annular passage where it is mixed with a secondary fluid or catalyst.
The internal mix is formed as a cartridge which can be part of a spray gun or a separate cartridge that can be added to reexisting guns to convert an external mixture to an internal mixer.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.